Nodular iron manufacture



United States PatentO NODULAR IRON MANUFACTURE Harold N. Bogart, Detroit, Mich., assignor to Ford Motor Company, Dearborn, Mich.,a corporation of Delaware No Drawing. Application November '7, 1955 Serial No. 545,531

.5 Claims. ((31-75-130) This invention is addressed to those interested in' ferrous metallurgy and will be found to be of especial interest to the metallurgist engaged in the manufacture of nodular cast iron. Nodular cast iron has attained great prominence in the ferrousmetallurgy field in recent years and is characterized by an as-cast structure in which thegraphitic carbon is in a round or nodular form as opposed to the graphitic flake usually associated with grey cast iron.

The manufacture of nodular cast iron usually involves the preparation of a low sulfur high carbon liquid grey cast iron composition to which is added usually in the ladle a ferro-alloy containing magnesium or cerium .followed by an inoculation with ferro-silicon. This double treatment causes the precipitation of the graphitic carbon in the nodular form upon solidification and results in much higher physical properties than can be attained from conventional grey iron. By judicious manipulation of the silicon content the matrix may be made all pearlitic or all ferritic or any desired intermediate structure.

This invention is specifically aimed at a reduction in the overall cost of producing nodular iron by altering-the inoculation procedure so that all or at least a portion of the ferro-silicon inoculant may be added in the molten form as opposed to the solid ferro-silicon which has been universally employed 'to date. In using solid ferro-silicon additions the art has found it necessary to employ ferrosilicon having a high silicon content to enable the addition of the requisite amount of silicon without unduly chilling the metal. When the silicon is added in the form of a molten iron silicon alloy, the silicon content of the alloy can be much lower inasmuch as no substantial amount of heat is abstracted from the metal by the addition. In fact, under some circumstances, the ferrosilicon may be heated sulfi'ciently to add to the temperature of the base metal. The cost of producing ironsilicon alloys, either molten or solid, goes up rapidly with the silicon content. Accordingly, it is much more economical to add a given amount of silicon as a low silicon content iron silicon alloy than as the higher grades of ferrosilicon.

As a specific example of the execution of this process a molten base iron was prepared in a standard three phase direct arc furnace. This alloy contained about 4 percent of carbon, .60 percent manganese, about 2 percent of silicon with minor amounts of phosphorus and a quite low sulfur content.

This furnace has been designated as C furnace in the data which follows. A second alloy Was prepared in a Detroit rocking furnace (indirect arc furnace). This furnace was designated B furnace and was charged with 35 pounds of charcoal pig and 70 pounds of 16 percent silvery pig to give a bath having a silicon content of about percent. From these two batches of molten metal eleven compositions were prepared as follows:

(1) Base iron in C furnace, carbide slag: 350# charcoal pig+1% Mn and .15 Cr.

ice

: 2 (2) Alloy in B furnace: 35# charcoal pig, 70 lbs. silvery pig (16% 100% Si approx.

lots were made up by combining .1 and 2 in varying proportions as indicated, with and without afinal solid inoculant. Test bars and fractures were cast.

Control: 50# from C 3 furnace, added solid FeSi, .15 Mg as MgCeFeSi; added .3% silicon (solid).

(11) 45# from .C furnace, :added .1-5%

MgCeFeSi; added.5# from B furnace.

(b) Added .2% solid FeSi to balance of (a).

( c) 42# from C furnace, added .15

,MgCeFeSi, added 8# from B" furnace.

(d) Added .2% solid FeSi to balance of.i(c).

(e) 39# from C .furnace, added .15

'MgCeFeSi, added ll# from B furnace.

(f) Added .2% solid FeSi to balance of (e).

(g) 364? from C furnace, added .15%

MgCeFeSi; added 14# from B furnace.

(h) Added .2% solid FeSi to balance of (g).

(i) 33# from C furnace, added .15%

MgCeFeSi; added 17# fromB furnace.

(j) Added .2% solid FeSi to balance of (i).

Test bars were produced from each of these eleven compositions and these test bars were fractured and also polished andetched with the following results:

Mg as .Mg as .Mg tas Mg .as

increasing silicon. Some e. 98% nodular (expL), -70% ferritic. f. tendency to flotation in 50-90% nodular (expL), %,ierritic.

n samples with solid in- 95-98% nodular (expL), 60%ierritic.

oculation. -98% nodular (expL), territic.

98% nodular, 85-90% terrific. 50-90% nodular(expl.), 90% ferritic.

Each of these compositions were also fabricated into tensile test bars and tested with the following results:

Physical properties ,Percent- Yield Tensile -a'ge strength strength 'elongation Control 55, 800 106, 000 .6 a 59, 000 86; 000 '4 b 60, 200, 89; 500 l 7 62, 000 87, 000 -6 63,000 88,500 8 69,400 93, 500 .6 73, 800 I 93, 000 .s 76, 000 2,000 "2 80, 000 96, 100 2 86, 700 89, 500 0 89, 000 98, 500 l Reduc- Young's tion of modulus area The chemistry of these bars is as follows:

Chemistry as a s-r z t t es s s sm C(Obhbk 'Astudy of the above data Will demonstrate that it is readily possible to fabricate commercially acceptable and substantially'completely nodular iron using molten ferrosilicon as the inoculant. The last several alloys are too high in silicon for most commercial usage and this high silicon is reflected in the low elongation and reduction in area in'values. However, all of these specimens exhibit a Youngs modulus of 23 or 24 million pounds per square inch which is very high for this class of material. All of these tests were made on unheat treated or as cast specimens.

While magnesium and cerium have been disclosed as the preferred initial inoculating agents, the invention is not so limited. Any of the divers inoculants disclosed in the nodular iron literature may be employed.

While a ten percent silicon content of the molten additive has been disclosed above, commercial considerations will usually dictate a somewhat lower silicon content, probably in the range of six percent of silicon. However, if weighing operations can be conducted accurately and the cost of higher grades of ferro-silicon is not a factor, any available ferro-silicon may be used. Circumstances favoring a high ratio of base metal to ferroalloy is a high silicon content of the base metal, a high silicon ferro-silicon and a high silicon content in the cerium or magnesium containing additive. Under extreme conditions this ratio may be as high as twenty to one. Ordinary commercial production aimed at a three per cent silicon content in the final casting and employing a six percent silicon ferro-silicon calculates to slightly more than two parts of base metal to one part of ferrosilicon.

In the above description reference has been made to term alloys containing a nodularizing agent. These are usually preferable for economic reasons although other non-ferrous, nodularizing agents such as magnesium nickel or magnesium copper may be employed if special circumstances warrant.

I claim as my invention:

1. The process of producing nodular iron castings comprising preparing a molten alloy comprising iron, silicon and carbon of such composition that if cast without inoculation would solidify to yield ordinary flake graphite containing grey iron, adding to this molten alloy a solid ferro-alloy containing a nodularizing agent, and then adding to the combination a molten ferro-alloy containing a substantial amount of silicon and a solid alloy containing a substantial amount of silicon whereby the entire molten mass is caused to solidify with the graphitic carbon in the nodular form.

2. The process of producing nodular iron castings comprising preparing a molten alloy comprising iron, silicon and carbon of such composition that if cast without inoculation would solidify to yield ordinary flake graphite containing grey iron, adding to this molten alloy a solid ferro-alloy containing a nodularizing agent selected from the group consisting of cerium and magnesium and alloys of cerium and magnesium adding to the combination a molten ferro-alloy containing a substantial amount of silicon and a solid alloy containing a substantial amount of silicon whereby the entire molten mass is caused to solidify with the graphitic carbon in the nodular form.

3. The process of producing nodular iron castings comprising preparing a molten alloy comprising iron, silicon and carbon of such composition that if cast without inoculation would solidify to yield ordinary flake graphite containing grey iron, adding to-this molten alloy a solid ferro-alloy containing a nodularizing agent, and then adding to the combination approximately one ninth of its weight of a molten ferro-alloy containing a substantial amount of silicon and a solid alloy containing a substantial amount of silicon whereby the entire molten mass is caused to solidify with the graphitic carbon in the nodular form.

4. The process of producing nodular iron castings comprising preparing a molten alloy comprising iron, silicon and carbon of such composition that if cast without inoculation would solidify to yield ordinary flake graphite containing grey iron, adding to this molten alloy a ferroalloy containing a nodularizing agent and a molten ferroalloy containing a substantial amount of silicon and a solid alloy containing a substantial amount of silicon whereby the entire molten mass is caused to solidify with the graphitic carbon in the nodular form.

5. The process of producing nodular iron castings comprising preparing a molten alloy comprising iron, silicon and carbon of such composition that if cast without inoculation would solidify to yield ordinary flake graphite containing grey iron, adding to this molten alloy a solid nodularizing agent, and then adding to the combination a molten ferro-alloy containing a substantial amount of silicon and a solid alloy containing a substantial amount of silicon whereby the entire molten mass is caused to solidify with the graphitic carbon in the nodular form.

References Cited in the file of this patent UNITED STATES PATENTS 342,869 Hadfield June 1, 1886 1,061,363 Hadfield May 13, 1913 2,485,760 Millis et al. Oct. 25, 1949 2,527,037 Smalley Oct. 24, 1950 

1. THE RPOCESS OF PRODUCING NODULAR IRON CASTING COMPRISING PREPARING A MOLTEN ALLOY COMPRISING IRON, SILICON AND CARBON OF SUCH COMPOSITION THAT IF CAST WITHOUT INOCULATION WOULD SOLIDIFY TO YIELD ORDINARY FLAKE GRAPHITE CONTAINING GREY IRON, ADDING TO THIS MOLTEN ALLOY A SOLID FERRO-ALLOY CONTAINING A NODULARIZING AGENT, AND THEN ADDING TO THE COMBINATION A MOLTEN FERRO-ALLOY CONTAINING A SUBSTANTIAL AMOUNT OF SILICON AND A SOLID ALLOY CONTAINING A SUBSTANTIAL AMOUNT OF SILICON WHEREBY THE ENTIRE MOLTEN MASS IS CAUSED TO SOLIDIFY WITH THE GRAPHITIC CARBON IN THE NODULAR FORM. 